iRhythm Holdings has announced results from two real-world retrospective analyses in post-ablation and pregnancy patient populations presented at the 2026 Heart Rhythm Society (HRS) annual meeting (23–26 April, Chicago, USA).
Across both studies, arrhythmias were detected beyond 48 hours and within 14 days in a large proportion of patients—30% of recurrent atrial fibrillation (AF) and 60% of arrhythmias in pregnancy—with important implications for clinical assessment and decision-making, according to the company. Additionally, iRhythm says these findings add to the body of evidence on the limitations of commonly used short-duration 24–48-hour Holter monitoring, and further reinforce the clinical value of continuous, uninterrupted monitoring up to 14 days with the company’s Zio ambulatory electrocardiogram (ECG) devices across diverse patient populations.
The first of the two aforementioned studies involved a nationwide retrospective analysis of 11,051 patients who were monitored with a Zio ambulatory ECG device in the year following AF ablation. Within this analysis, the overall recurrence rate of AF was 21%, and a substantial proportion of AF recurrence was detected beyond 48 hours and within 14 days.
According to iRhythm, one notable finding was the fact that AF recurrence would often be missed with 24–48-hour monitoring. With up to 14 days of continuous, uninterrupted monitoring using Zio ambulatory ECG, 26% of patients overall—and 29.8% of patients with paroxysmal AF—had their first detected AF recurrence beyond 48 hours, indicating that reliance on short-duration Holter monitoring would miss AF recurrence in a considerable proportion of post-ablation patients.
The data also suggest that up to one in four patients with true AF recurrence could be misclassified as a false negative with short-duration Holter monitoring compared up to 14 days with Zio ambulatory ECG.
“These data reinforce that monitoring approach and duration directly impact what is detected—and what is missed,” said Mintu Turakhia, chief medical and scientific officer and executive vice president of advanced technologies at iRhythm. “Monitoring of 48 hours or less leads to false negatives of AF recurrence in 30% of those monitored in the year following PVI [pulmonary vein isolation]. As AF burden and recurrence increase the risk of stroke—and are directly actionable for clinical decisions regarding anticoagulation, antiarrhythmic, repeat ablation, and risk of heart failure—the data are clear that 14 days should be the minimum threshold for post-ablation monitoring.”
As per the second study presented at HRS 2026, in a retrospective analysis of 486 pregnant patients undergoing extended monitoring using Zio ambulatory ECG devices, arrhythmias were present in one in seven patients, but with 60% first detected after 48 hours—events that would be missed with commonly used short-duration 24–48-hour Holter monitoring.
According to iRhythm, arrhythmias were detected in 37.7% of pregnant patients, the majority evaluated for symptoms like palpitations (62.8%), showing that rhythm abnormalities can occur even in patients without structural or other forms of heart disease. Furthermore, clinically significant arrhythmias were detected in 13.6% of patients, including AF ≥30 seconds, supraventricular tachycardia (SVT) ≥90bpm and ≥30 seconds, ventricular tachycardia (VT) ≥100bpm and ≥4 beats, pause ≥3 seconds, and atrioventricular (AV) block.
Most arrhythmias—66.7% clinically significant and 59.6% overall—were detected after 48 hours. These data suggest that short-duration 24–48-hour Holter monitoring would fail to detect a substantial portion of clinically significant arrhythmias compared to up to 14 days of continuous, uninterrupted monitoring with Zio ambulatory ECG devices, iRhythm claims. Finally, the median analysable time was 99.2%, indicating that nearly all recorded monitoring time produced usable heart rhythm data, demonstrating that high-quality ECG data can be obtained with continuous, uninterrupted monitoring up to 14 days with Zio ambulatory ECG devices in pregnant patients.
“Physiologic changes during pregnancy increase arrhythmia risk, with implications for both maternal and foetal health,” said Ridhima Kapoor (Stanford University, Stanford, USA), an investigator on the study and its presenting author. “This analysis demonstrates that arrhythmias occur in more than one-third of pregnant patients, with clinically significant events in nearly one in seven. Notably, the majority were identified after 48 hours of monitoring. This underscores the importance of extended cardiac monitoring to accurately capture arrhythmia burden and guide management.”
iRhythm concludes that the data presented at HRS 2026 add to its comprehensive clinical evidence programme encompassing more than 140 original research manuscripts, insights derived from over three billion hours of curated heartbeat data, and over 12 million patient reports since the company’s inception.
